A plant of this kind comprises an apparatus such as is known from EP-A 0 780 917 (=P.6719). This apparatus contains a cell block with fuel cells which is surrounded by a heat insulating sleeve. An afterburner chamber is located between the sleeve and the cell block. A reformer for the treatment of a fuel gas (also called a pre-reformer) is arranged in the sleeve. It is connected to a heat exchanger, by means of which heat for the endothermic reforming process can be supplied to it from the exhaust gases.
In the reforming of the fuel gas, which consists mainly of methane in many applications, the latter is catalytically converted at least partially into CO and H.sub.2 in the presence of H.sub.2 O and with process heat being supplied. Instead of a gaseous fuel a liquid one can be provided, with it however being possible for the use of a liquid fuel to be connected with additional problems, in that the latter must be fed into the reformer in a suitable manner.